The present invention relates to control of plant-virus diseases by applying as an active ingredient a chemical compound represented by the general formula: ##STR1## wherein R denotes an alkyl group having 3 to 18 carbon atomed; R' denotes a hydrogen atom or a glycopyranosyl group; p denotes an integer of one or 2; q denotes also one or 2, provided p+q=3; r denotes also one or 2; and s denotes 0 or one, provided r+s=1 or 2, or a salt thereof on the plant to be protected from the plant-virus.
Hitherto, various crops cultivated in fields and in various facilities, for instance, tobacco, tomato, cucumber, strawberry, Japanese radish, potato, Chinese cabbage, piment, etc. have been suffered a very large damage from plant viruses. Intensification of and reducing the man-power in agriculture are very critical in increasing the damage moreover. In spite of the strong demand of the breeding resistant varieties and the development of anti-virus agents, the situation is now quite unsatisfactory.
That is, the controlling of plant virus diseases has hitherto been carried out by pulling out the plants suffering from the disease or by controlling the vectors of plant viruses such as aphids, leafhoppers, planthoppers, nematodes. However, since these methods cannot positively control the plant virus diseases, the development of the agents effective in directly controlling the plant viruses themselves has been eagerly desired. As substances which are physiologically active against plant virus diseases, anti-metabolites such as 2-thiouracil, 5-fluorouracil, 8-azaquanine, etc., antibiotics such as blasticidin S, formycin B, aabomycin A, etc., polysaccharides and proteins produced by micro-organisms and polysaccharides, proteins and tannins derived from plants have been known. Of these substances, anti-metabolites and antibiotics have drawbacks such as giving phytotoxity to plants and having no persistency, and polysaccharides, proteins, tannins, etc. have defects of not inhibiting the infection of the viruses by vectors such as aphids.
The inventors, in considering the above-mentioned situations, have studied to find an effective compound against a wide variety of plant virus diseases such as cucumber mosaic virus disease, tobacco mosaic virus disease, etc., which is not phytotoxic to plant body and is safe to human and useful animals. As a result, the inventors have found that the compound shown as above in the formula (1) and its salt answer the above-mentioned purpose, and then completed the present invention.
Accordingly, the purpose of the present invention is to effectively control not only the plant-virus diseases infected by plant sap but also the plant-virus infected by vectors without giving any phytotoxic action on the plants to be protected from such plant virus diseases. The other purposes will become apparent in the ensuing specification and claims.